(1) Field of the Invention
This invention relates to a surface light source structure, and more particularly relates to a surface light source structure applied in a backlight module of a flat panel display.
(2) Description of the Prior Art
In present, light emitting diode (LED) with the advantages of small size and low power consumption has replaced traditional cold cathode fluorescent lamp (CCFL), and has become a mainstream product applied in the backlight module of the flat panel display.
FIGS. 1A and 1B depict two popular embodiments using LED as a light source of the flat panel display. One is to assemble the LEDs 22 beside the edge of the backlight module 20 for projecting light traversing the backlight module 20. The traversing light is transformed into upward light by reflection and refraction and then projected to the display panel 10. The other is to assemble the LEDs 32 under the backlight module 30 for projecting light upward and penetrating the backlight module 30 to the display panel 10.
Generally, the embodiment assembling LEDs 22 beside the edge of the backlight module 20 reduces the number of LEDs 22 and simplifies related circuit design, however, the uniformity of the surface light generate by the backlight module 20 is hard to be controlled. For example, the location near the LEDs 22 usually has greater brightness. Thus, this embodiment is mainly adapted to small-size display. In contrast, although the embodiment assembling LEDs 32 under the backlight module 30 in array has a complicated circuit design, the backlight module 30 is capable to provide uniform surface light illuminating the display panel 10.
FIG. 2A is a schematic view showing a traditional surface light source structure 100 applied in the backlight module. FIG. 2B is a circuit diagram of the surface light source structure 100. As shown, the surface light source structure 100 has a circuit board 120 and a light emitting diode (LED) array 140. The circuit board 120 has a conductive pattern 122 formed thereon. The LED array 140 is assembled on the circuit board 120. The LED units 142 of the LED array 140 are connected to each other through the conductive pattern 122 on the circuit board 120. The LED units 142 of the same row are connected in series. The rear ends of every two neighboring LED rows (right end in the figure) are electrically connected to each other. Meanwhile, the front ends of the two neighboring LED rows are connected to a positive electrode 150 and a negative electrode 160 respectively. That is, the LED units 142 of the two neighboring LED rows are connected in series between the positive electrode 150 and the negative electrode 160 which are located on the same edge of the circuit board 120.
Since the LED array 140 features two neighboring LED rows connected in series, the LED array 140 must have even LED rows, which creates an additional limitation toward the circuit design of the circuit board 120 and the layout of the LED units 142. In addition, the number of LED units 142 connected in series between the positive electrode 150 and the negative electrode 160 is the number of columns of the LED array 140 multiplies two. The increasing of LED units 142 connected in series may badly affect the uniformity of the LED units 142 and make the LED array 140 difficult to control.
FIG. 3A is a schematic view showing another traditional surface light source structure 200 applied in the backlight module. FIG. 3B is a circuit diagram of the surface light source structure 200. As shown, the surface light source structure 200 has a circuit board 220 and an LED array 240. The circuit board 220 has a conductive pattern 222 formed thereon. The LED array 240 is assembled on the circuit board 220. The LED units 242 of the LED array 240 are connected to each other through the conductive pattern 222 on the circuit board 220. The LED units 242 of the same row are connected in series. In addition, every rows of the LED array 240 are connected between a positive electrode 250 and a negative electrode 260 in parallel. The positive electrode 250 and the negative electrode 260 are located on the opposite edges of the circuit board 220.
In contrast to the surface light source structure 100 of FIG. 2A, the number of the LED units 242 connected in series in the surface light source structure 200 is identical to the number of columns of the LED array 240. In addition, the LED array 240 may have a design of using odd LED rows. Nevertheless, the positive-to-negative directions of all the LED units 142 of the LED array 240 are identical, which is the direction from the left side of the circuit board 220 to the right side in the figure. However, if the positive-to-negative directions of all the LED units 242 of the LED array 240 are identical, the uniformity of the resulted white light would be badly influenced by the layout of the LED chips 242G, 242R, 242B on the LED unit 242. For example, the LED unit 242 in the figure has a green, a red, and a blue LED chips 242G, 242R, 242B arranged from the top down in sequence to generate white light. The light of the surface light source structure 200 may be greener near the upper side but bluer near the lower side. In order to solve this problem, referring to FIG. 3C, a typical method is to adapt different LED units 242a, 242b in the neighboring LED rows 241a, 241b. For example, the LED units 242a of the first LED row 241a has a green, a red, and a blue LED chips 242G, 242R, 242B arranged from the top down in sequence, and the LED units 242b of the second LED row 241b has a blue, a red, and a green LED chips 242B, 242R, 242G arranged from the top down in sequence so as to compensate the light provided by the LED units 242a. However, the design using different LED units 242a, 242b increases fabrication cost.
The arrangement of LED arrays 140, 240 of the above mentioned surface light source structures 100,200 have their drawbacks. Accordingly, a surface light source structure is provided in the present invention, which does not need to use different LED units, reduces the number of LED units connected in series, and also enhances the uniformity of light.